1. Field of the Invention
This invention relates to the mounting of circuit boards within housings of portable electronic devices and, more particularly, to a method for mounting a system board within a laptop computer to prevent damage to the connections between the board and components mounted thereon due to the warping of the system board.
2. Summary of the Background Art
The system board of a laptop computer includes a number of circuit modules attached to the board by mechanical and electrical connections, such as the solder balls of a ball grid array, that are susceptible to damage by warping the system board in the region of the components. Such warpage may occur due to the warping of the case of the laptop computer, to which the system board is attached, when the laptop computer is jammed into a small space, such as a student's backpack, with other items. Furthermore, damage to such electrical connections may occur when a circuit board warped during its manufacture is forced into a flattened condition as it is rigidly mounted within the case of the laptop computer.
A number of components within computer systems have been mounted by means of resilient materials applied to reduce the effects of shock loads applied to the case of the system on the components, regardless of the directions in which the shock loadings are applied. Such mounting means provides for the deflection of the internal component in any direction relative to the surrounding structures. When such methods are applied to a system board, the resulting resilience of movement in all directions results in an undesirably spongy feel when the user attaches cables to connectors mounted on the circuit board. Furthermore, the allowed movements of the system board by such mounting may result in the misalignment of switches, key buttons, indicator lights, etc., that need to be aligned with features of the cover, such as cutouts. Thus, what is needed is a method for mounting a circuit board to allow motion against resilient surfaces perpendicular to the surfaces of the circuit board while restricting movement of the circuit board in directions parallel to its surfaces.
The covers of portable electronic devices are usually composed to plastic materials because of the low weight and other desirable features of such materials. Because of the difficulties associated with forming satisfactory screw threads in plastic materials, metallic threaded inserts may be included in plastic covers to receive screws holding the covers together or attaching internal components to the covers. These inserts may be molded in the plastic material when a cover is made, or they may be attached within holes by ultrasonic insertion or by the expansion of the insert as an internal part is moved to hold the insert in place. What is needed is an insert that can be used both to provide a threaded hole to receive a screw and a guiding surface along which a circuit board can move during compression of associated resilient mounting elements.
The patent literature includes a number of examples of resiliently mounted circuit boards within portable electronic devices. For example, Japanese Patent JP5315772 describes a portable electronic device including a circuit board mounted between covers in a manner chosen to prevent the board from cracking due to shock when the device is dropped. In one embodiment, a rubber grommet extends through a hole in the circuit board near its corner, with a bushing extending through a hole in the grommet. A flange of the bushing engages a post forming a portion of the lower cover. A screw extends through a hole in the bushing to hold a post forming a portion of the upper cover against the upper end of the bushing. The grommet includes an upper portion compressed between the post of the upper cover and the circuit board, a lower portion compressed between the post of the lower cover and the circuit board, and a central portion held between the hole within the circuit board and the bushing. In this way, the circuit board is allowed to move in all directions against the resilient surfaces of the grommet. What is needed is a surface limiting such movement in directions parallel to the surfaces of the circuit board.
U.S. Pat. No. 6,399,888 describes a device for buffering and supporting a circuit board, with the device including a lower flexible supporter and an upper buckle head, which is configured to engage a hole of the circuit board, being formed with a number of forked elastic wings to abut against a surface of the circuit board. The flexible supporter has a plate and at least one flexible support portion that is formed, alternatively, by a single integrally formed flexible supporter or a pair of cambered or straight flexible support pieces. Again, what is needed is a structure limiting movement of the circuit board in directions parallel to its surfaces.
U.S. Pat. No. 6,012,041 and U.S. Pat. App. Pub. No. 2002/0149916 describes electronic devices having additional support members placed to extend between circuit boards and housing surfaces, in order to use the structure of the housing to limit the deflection of the circuit board due to impact or vibration. In the device of U.S. Pat. No. 6,012,041, a shock-absorbing member extends between the circuit board, on which a hard disk drive is mounted, and the chassis or housing. In the device of U.S. Pat. App. Pub. No. 2002/0149916, the device includes electrical contact elements that are electrically connected to a plug-in part, having ends in the housing interior that run parallel to each other, protruding toward an opening in the housing, so that the ends pass through contact openings of the circuit board as the circuit board is installed through the opening, being connected conductively to the circuit board. To protect impact-sensitive and vibration-sensitive components, part of the length of the contact elements not inserted into the contact openings is provided with elastically deformable segments, so that the circuit board is flexibly supported in the housing by the contact elements. While such additional support elements extending between the circuit board and the housing reduce deflections of the circuit board caused by the application of shock and vibration to the mass of the circuit board, these supports do not reduce warping of the circuit board caused by the warping of the housing itself as the device is jammed into a confined space with other items.
The patent literature additionally includes a number of descriptions of devices other than circuit boards that are resiliently mounted within portable electronic apparatus. For example, U.S. Pat. No. 6,275,352 describes a disc drive including a plurality of isolation devices that are integrated into a base deck at standard locations for receiving screws, with each of the isolation devices allowing movement of the disc drive at its location in all directions. U.S. Pat. No. 6,115,259 describes a vibration isolating mounting system for tuner elements including grommet-like elements that are deployed within slotted holes in a plate mounting the tuner elements and in the chassis of a television system. Movement is allowed in all directions to isolate the tuner elements from environmental vibrations that could otherwise affect their performance. While such movement is not a problem for disc drives or for the tuner elements, it presents problems when an isolation device is applied to a circuit board to which external connections must be made, or to a circuit board having elements that need to be aligned with features of the housing or cover.
U.S. Pat. No. 6,633,489 describes a method for preventing or minimizing cracking of the ceramic body of a microprocessor processor chip by maintaining the microprocessor chip in a desired relationship with a circuit board while limiting the transmission of shock and vibrating motion to the chip. The microprocessor chip is attached to the circuit board by a dynamic isolating mount that is maintained in a compressed state. However, what is still needed is a method for preventing damage caused by the application of static forces to warp the circuit board as the electronic device including the circuit board is placed in a confined space with other objects.